Recently, more and more electronic equipments become to be installed in a DVD/BD recorder, a television, a portable equipment or the like. Moreover, the precision of the installed electronic equipment is improved. Demands on reliability of the electronic equipment are continuously increasing. It is required a low-price and reduced-size acceleration sensor having high output sensitivity of 100 mV/G or more in order to detect impact applied to the electronic equipment or vibration which the electronic equipment itself generates.
As for a means to detect acceleration, various methods are conventionally suggested or put into use. Especially, a bending-type piezoelectric acceleration sensor (hereinafter, simply refers to as “a piezoelectric acceleration sensor”), which uses bending of a piezoelectric ceramics, is uses extensively because of its simple structure and easiness to reduce its price.
Output sensitivity which results from the bending of the piezoelectric ceramics is theoretically limited to about a few mV/G at most. Therefore, it is necessary to amplify the output from the piezoelectric ceramics finally so as to obtain output sensitivity of 100 mV/G or more. Moreover, it is important to amplify the output sensitivity while keeping the size of the piezoelectric ceramics small.
Because of this, various structures to support piezoelectric ceramics are suggested. For example, a piezoelectric ceramics of Patent Document 1 is supported in a cantilever structure by a side surface of a storage case. A piezoelectric ceramics of Patent Document 2 is supported in a both-ends support structure by a bottom surface of a storage case. Patent Document 3 discloses a technology that the vicinity of each of opposite ends of a piezoelectric vibrator and the middle part of the piezoelectric vibrator are polarized in opposite directions to each other. Moreover, the piezoelectric vibrator is supported in a both-ends support structure so that output sensitivity is improved.